1. Field of the Invention
The present invention generally relates to a device used in a patient interface assembly to connect a headgear and a patient interface device, such as a mask, and to a system for supplying a flow of gas to a patient.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, which varies with the patient's respiratory cycle or the patient's condition, to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), cheynes-stokes respiration, or congestive heart failure.
Non-invasive ventilation and pressure support therapies involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask, on the face of a patient to interface the ventilator or pressure support device with the airway of the patient so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such masks on the face of a patient by means of a headgear worn on the patient's head. A typical headgear assembly includes upper and lower straps, each having opposite ends that thread through connecting elements provided on the opposite sides of the mask. Because such masks are typically worn for an extended period of time, it is important the headgear maintain the mask in a tight enough seal against a patient's face without discomfort.
One such headgear is disclosed in U.S. Pat. No. 5,517,986. The headgear includes a cap-like headpiece adapted to fit the crown and back of a patient's head. Lower straps provide a two-point connection with a gas delivery mask. Additionally, a pair of upper straps can be used to provide a four-point connection with the gas delivery mask if needed. In order to secure the mask in place on a patient's head, each strap passes through an elongated opening on the mask and then bends back on itself to hold in place with hook and loop material. The patient adjusts the length of material that passes through the opening to secure a good fit of the mask. However, if the mask is removed, the adjustment process must be repeated.
Another known mask and headgear connector arrangement is disclosed in International Publication No. WO 00/78383 A1 (“the '383 application”). In this arrangement, a respiratory mask has a rigid frame having first and second female connectors integrally molded thereto. The female connectors receive male connectors connected to the headgear straps. The female connectors are locked into a single discrete location when engaged. Because the connectors do not swivel independently, the user must take care to ensure that each strap is not twisted when the connectors are engaged. If a strap does become twisted, the user must disconnect the male connectors, straighten the strap and reconnect the male connectors, otherwise the twist of the strap may dislodge the mask from the user.
Published European patent application publication no. EP 0958841 A2 (application no. 99108650.5) discloses a mask and headgear connection assembly that is similar in function to that disclosed in the '383 application. In the European application, loops are provided at the end of the headgear straps and corresponding hooks are provided on the mask shell. This configuration allows the user the easily detach the headgear straps from the mask by removing the loops from the hooks. However, this hook and loop configuration suffers from the same disadvantage as that of the '383 application. Namely, it does not allow the connectors to swivel independently so that twisting of the headgear straps can deteriorate the usefulness of the mask.